BP Plc agreed to pay $10.5 billion, its biggest acquisition in almost two decades, for most of BHP Billiton Ltd.’s onshore U.S. oil and natural gas assets, including in the prized Permian Basin.

The deal gives the London-based energy giant a position in the Permian, a swathe of west Texas and New Meixco that’s the world’s fastest-growing major oil region. It’s another sign that Big Oil has mostly rebounded from the 2014 to 2016 price crash. BP will also add positions in the Eagle Ford and Haynesville basins in Texas and Louisiana.

“We’ve just got access to some of the best acreage in some of the best basins in the onshore U.S.,” BP’s Upstream Chief Executive Officer Bernard Looney said in a statement. The Permian produces about 3.4 million barrels a day, which would make it the fourth-largest member of OPEC, behind Saudi Arabia, Iraq and Iran.

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BP shares reacted negatively to the transaction, falling as much as 2.4 percent in London. BHP appears to have got the better side of the deal, selling the entire package of assets for a higher price than expected, RBC analyst Biraj Borkhataria said in a note.

Rising oil prices have boosted prospects for shale sector deals, while the Permian is a focus for industry consolidation as technological advances allow explorers to drill ever-longer sideways wells. Concho Resources Inc. agreed in March to acquire RSP Permian Inc., while Exxon Mobil Corp. bought drilling rights for about $6 billion last year.

“The Permian is the largest U.S. shale play with the most inventory so it’s not hard to see the long-term attraction,” said Leo Mariani, an Austin-based analyst at NatAlliance Securities LLC.